A decoupled heave and roll suspension that ran at Formula Bharat 2020

Problem

With four corner spring-dampers, one set of springs and dampers carries both heave and roll, so a setting that suits one compromises the other. A decoupled layout gives each mode its own spring and damper, so heave and roll stiffness and damping can be set independently. Nobody in the team had built one.

Approach

Rockers split the motion: a heave element works when the wheels move together, a roll element when they move in opposition (Fig. 2), each with its own motion ratio. I placed the geometry in a full-car MSC Adams model and set the two ratios there (Fig. 1). For the roll element I designed a damper cage that always compresses its spring-damper, whether the rocker pulls it apart or pushes it together (Fig. 3).

What I did

• Designed the decoupled layout, with independent heave and roll damping.
• Designed the damper cage, so a standard spring-damper gives the roll stiffness in both directions of roll, and a later iteration on linear bearings and low-friction joints, for more precise motion.
• Built the full-car kinematic model in MSC Adams from scratch, because no template supported the geometry, cross-checked it in Lotus Suspension Analysis, and used it to set roll-centre migration, camber gain, bump steer and motion ratios.
• Ran FEA on every major suspension part, from the rockers and uprights to the wheel centres, across 5 to 10 load cases each: maximum cornering, braking, acceleration, heave and combined (Figs. 4 and 5).
• Took mass out of the unsprung wheel centres and, inboard, the damper cage, the damper extension shaft and the rocker shafts.
• Designed the welding fixtures (Fig. 6); the team did its own part design, design for manufacture, bearing and fastener selection.